Microalgae Cultivation In Photobioreactor Research Articles

Microalgae cultivation in photobioreactors: An overview of light characteristics

There is increasing commercial interest in the cultivation of microalgae for the production of biofuels, foods, pharmaceuticals, and wastewater treatment. Light is one of the most important factors for the growth and product yield from photosynthetic cells. In this review, light transfer and photosynthesis in algal cells, and the issues of light utilization in the cultivation of microalgae in photobioreactor (PBR) are discussed. Research progress on the improvement of light utilization in microalgae cultivation is outlined. In addition, PBR design assisted by computational fluid dynamics and a strong focus on improving the light characteristics in the scale‐up of PBRs is emphasized.

Characteristics of light regime on biofixation of carbon dioxide and growth of Scenedesmus obliquus with light-emitting diodes

Light regime is one of the key factors affecting the growth and carbon dioxide fixation rate of microalgae. The results of this study demonstrated that light intensity, light duration, and light quality are significant factors to control the biomass growth and carbon dioxide fixation of Scenedesmus obliquus. The optimal light intensity for S. obliquus obtained in this study is 13 000 Lux. The maximum biomass concentration and carbon dioxide fixation rate during different light cycles were 0.992 g · l−1 and 0.326 g · L−1 · d−1 obtained under continuous illumination, respectively. The white light, resulting in higher biomass concentration than the other light, indicated that sunlight is a promising light source for the culture of microalgae. This study will provide valuable information of light regime for the cultivation of microalgae in photobioreactors.

Mathematical model of the CO2 solubilisation reaction rates developed for the study of photobioreactors

The transfer of CO2 between the gas and liquid phases is one of the most important processes that occur during cultivation of microalgae in photobioreactors. A key factor that influences the rate of mass transfer is the concentration of CO2 in the liquid phase, which, in turn, depends on the rates of the reactions involved in CO2 solubilisation. This work presents a mathematical model for the rate of these solubilisation reactions with correlations that allow the calculation of the model parameters at temperatures from 5°C to 40°C. The model was validated using data of CO2 mass transfer from the literature obtained with two experimental systems: a bubble column for CO2 absorption and a flat‐panel photobioreactor. The model was further used to show that the increase in the rate of CO2 absorption that occurs at higher pH values is due to increased consumption of CO2(aq) in the solubilisation reactions and not to an increase in kLa. The pH decreases as CO2 is solubilised, therefore, when pH is controlled, the mass transfer rate is higher than it would be without pH control. Our model can be used as a tool to guide the operation, control and scale‐up of photobioreactors for the cultivation of microalgae.

Modeling the light distribution in airlift photobioreactors under simultaneous external and internal illumination using the two-flux model

A simultaneous external and internal illumination method is proposed for cylindrical airlift photobioreactors in this paper, in which multiple light sources are placed around the downcomer region, to achieve a more homogeneous light distribution. Internal light sources are mounted near the wall of the draft tube and external light sources near the wall of the photobioreactor. The light distribution in an airlift photobioreactor under simultaneous external and internal illumination (APBR-SEII) with various biomass concentrations and radii is investigated using the two-flux model. This model is able to obtain reasonable prediction compared with the simulation of more rigorous DO models, and is suitable for real-time control of microalgae cultivation in photobioreactors. Light attenuation profiles are compared with those of only externally illuminated airlift photobioreactors (APBR-EI), showing that the new illumination method can increase the size of the illuminated zone in photobioreactors and enable a more uniform light distribution in the downcomer region. The calculation results also show that the annular distance of the downcomer region (ΔR) is more critical than the radius of the photobioreactor (R) to light distribution and therefore the design of photobioreactors. Asymmetry of light distribution in an airlift photobioreactor with the same radiation flux on the two walls is pronounced for low biomass concentrations and small radii.